A sodium-sulfur battery is used in a power storage device that supplies power to a power grid network and that receives power from the power grid network.
The sodium-sulfur battery is a secondary battery that operates at high temperatures. Accordingly, in the power storage device in which the sodium-sulfur battery is used, the sodium-sulfur battery is heated by a heater. Further, the temperature inside the power storage device must be the temperature at which devices operate stably. Therefore, the temperature inside the power storage device is adjusted by an air conditioner.
The power for allowing the heater and the air conditioner to operate is supplied from the power grid network. Accordingly, when the power reception from the power grid network is shut off because of power failure, maintenance or the like, the power is not supplied to the heater and the air conditioner. When the power is not supplied to the heater and the air conditioner, the temperature of the sodium-sulfur battery drops, and the temperature inside the power storage device deviates from the temperature at which equipment operates stably.
When the temperature of the sodium-sulfur battery drops, depending on the state of charge of the sodium-sulfur battery, the sodium-sulfur battery tends to fail because of distortion of components or the like. Further, when the temperature inside the power storage device deviates from the temperature at which the equipment operates stably, the equipment tends to fail.
Patent Document 1 proposes a solution to the problem. Patent Document 1 proposes that the sodium-sulfur battery or the like supply power to the heater when the power reception from the power grid network is shut off.